WASHINGTON (Reuters) - Breast cancer patients with lower
levels of vitamin D were far more likely to die and far more
likely to have their cancer spread than women with normal
levels, Canadian researchers reported on Thursday.

Women deficient in the "sunshine vitamin" when they were
diagnosed with breast cancer were 94 percent more likely to
have their cancer spread and were 73 percent more likely to die
than women with adequate vitamin D levels, the researchers
said.

More than three-quarters of women with breast cancer had a
vitamin D deficiency, the researchers reported to an upcoming
meeting of the American Society of Clinical Oncology.

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"The women with the lowest vitamin D levels had the highest
risk of death from breast cancer," Dr. Richard Schilsky, of the
University of Chicago and president-elect of ASCO, told Reuters
in an interview.

"We are seeing an association. It is possible that vitamin
D is simply a marker for healthy lifestyle. We don't think that
is the case," said Dr. Pamela Goodwin of Mount Sinai Hospital
in Toronto, who led the study.

The study adds to a growing body of evidence that vitamin
D, made when sunlight hits the skin and used to fortify many
foods including milk, is important for preventing chronic
diseases. It is key to maintaining strong bones.

Goodwin's team studied 512 women with a mean age of 50 with
newly diagnosed breast cancer treated at three University of
Toronto hospitals between 1989 and 1995. They were followed
until 2006, a median of just under 12 years.

Only 24 percent of the patients had adequate levels of
vitamin D when they were diagnosed with cancer.

EARLIER, MORE AGGRESSIVE CANCER

Goodwin said optimal levels are considered to be somewhere
between 80 and 110 or 120 nmol/L (nanomoles per liter) of
blood, although there are no standard guidelines. They
considered anything less than 50 nmol/L to be deficient.

After 10 years, cancer did not spread or come back in 83
percent of women with normal levels and 85 percent of these
women were still alive. But just 69 percent of women with low
vitamin D levels were cancer-free 10 years later and just 74
percent were still alive.

Women with low vitamin D levels were also likely to have
developed cancer before reaching menopause, had higher body
mass indexes -- a measure of being overweight -- had higher
insulin levels and had more aggressive tumors.

"It is something that is going to make us think a lot
harder about what the relationship is between vitamin D and
breast cancer," Schilsky said. "Vitamin D may turn out to be
far more important in cancer than we realized."

Associations have also been found between vitamin D and
prostate and colon cancer, they noted. And Goodwin said low
vitamin D levels had also been linked with heart disease.

Goodwin noted that her study had only found an association.
A randomized trial in which some women were assigned to take
vitamin D and others took placebos would be needed to prove
that it was in fact a lack of the vitamin causing the disease.

"It is really hard to know what a woman's vitamin D level
is now," Goodwin said in a telephone interview.

"That's why we have taken the fallback position to say at
least for breast cancers patients, they should talk to their
physician and get their vitamin D level checked," she added.

Both Goodwin and Schilsky stressed that it would be
important to avoid taking too much vitamin D, which can be
toxic. "We don't want to see women taking 10,000 IU a day,"
Goodwin said.